1. Field of the Invention
The invention relates in general to a method and apparatus for controlling an optical disc drive, and more particularly to a method and apparatus for controlling a tilt between an optical axis of an optical pick-up head and an optical disc.
2. Description of the Related Art
Along with the rapid advance in the multi-media industry in recent years, small-sized and high-capacity optical storage media such as CD, DVD, which store the data in a better condition and for a longer duration, have been widely used in the storage of audio/video data, back-up data, etc. With the growing popularity of optical disc, optical disc drive with optical disc accessing function is playing a greater role in the market of multi-media products.
Referring to FIG. 1, optical disc drive rotates an optical disc 106 along a specific direction 112 via a spindle motor 102, moves an optical pick-up head 104 along the radial direction 124 of the optical disc 106, and uses a laser beam emitted by the optical pick-up head 104 to scan the record surface of the optical disc 106 for accessing data. Ideally, when the data of the optical disc 106 are being read, the optical axis 122 of the optical pick-up head 104 is perpendicular to the optical disc 106, and thus the optical pick-up head 104 can precisely read the data stored in the optical disc 106. Refer to FIG. 2A, meanwhile, the laser spot 202, which is projected onto the record surface of the optical disc 106 for reading the recorded data 212, would have an even and centralized energy distribution.
However, in practical implementation, the optical disc 106 would deviate during the rotation, therefore preventing the optical axis 122 of the optical pick-up head 104 from maintaining perpendicular to the optical disc 106. Consequently, the laser beam projected onto the optical disc 106 would cause aberrations of the light spot such as spherical aberration, coma, astigmatism, field curvature, distortion, etc. The optical aberrations would deteriorate quality of optical paths and undermine the quality of electric signals, resulting in increase of data accessing errors.
The tilt between the optical axis 122 of the optical pick-up head 104 and the optical disc 106 can mainly be decomposed into tilts in two directions for the convenience of analysis and calibration: one is the tilt along the radial direction 124, and the other is the tilt along the tangential direction 126. Referring to FIG. 2B, the deviation in the tilt along the radial direction 124 would mainly cause the laser spot 204 projected onto the record surface of the optical disc 106 to have uneven energy distribution along the radial direction 124. Referring to FIG. 2C, the deviation in the tangential direction 126 would mainly cause the laser spot 206 projected onto the record surface of the optical disc 106 to have uneven energy distribution along the tangential direction 126.
Therefore, how to achieve a method for controlling the tilt between the optical axis of the optical pick-up head and the optical disc for the optical axis of the optical pick-up head to maintain at an optimal tilt in response to the optical disc has come to the fore.